This invention relates generally to a vibration system that efficiently transfers radial vibration from a vibration-inducing member to produce axial vibration in a vibratable member through a support member that filters out undesirable vibration. In preferred embodiments, a piezoelectric transducer imparts ultrasonic oscillation to a vibratable plate, particularly a vibrating aperture (orifice) plate of an aerosol generator device, wherein the vibrating plate is perforated with holes and is operable in a fluid medium. The invention may also useful in the field of ultrasonic wave transmission in a fluid medium including, but not limited to, underwater sonar, depth sonar and obstacle detecting sonar.
Devices wherein a circular aperture plate is vibrated using a piezoelectric transducer in the form of a ring are well-known in the art. For example, in Maehara U.S. Pat. No. 4,605,167, a vibratable plate having at least one nozzle opening therein is secured to a rigid housing and a piezoelectric ring is secured to the vibratable plate for inducing therein a displacement to discharge a small quantity of liquid through the nozzle opening. In other devices described in the art, a circular vibratable plate is directly bonded to the piezoelectric ring and covers the central opening in the piezoelectric ring; for example, as described in Toda U.S. Pat. No. 5,297,734. As other examples, Humberstone et al U.S. Pat. No. 5,518,179, Ross et al U.S. Pat. No. 5,261,601 and Davison et al U.S. Pat. No. 6,062,212 describe vibrating devices wherein a circular vibratable plate is mounted over the central opening of a thin annular member, or “washer”, which is bonded to a piezoelectric ring. When actuated, the piezoelectric ring vibrates radially to cause the washer to operate in a “bending mode” that vibrates the vibratable plate in the axial direction. When these types of devices are manufactured the components must be carefully aligned concentrically with each other when the vibratable plate is attached to the washer and the washer is positioned over the opening in the piezoelectric ring.
Installing an ultrasonic transducer directly onto a rigid frame or housing, such as taught by Maehara, is also problematic. The reason is that the entire body of the transducer vibrates, with some portions vibrating at a small amplitude and some portions vibrating at an amplified amplitude. When the transducer is installed on the rigid fixture, the oscillation amplitude is reduced. Another problem with prior art arrangements is that the piezoelectric ring naturally vibrates in 3 directions (i.e., X, Y and Z axes) and transmits such vibration to the vibrating plate. The vibrations that are transmitted to the plate are superimposed and the contribution of the axial vibration may be canceled or partially canceled out. It is therefore desirable to filter out the undesirable vibration of the piezoelectric element and to use only vibration in a single direction, e.g. the axial direction. Attempts to address this problem have included mounting the vibratable plate on resilient retainer members, or “fingers”, e.g. as described in Martens III et al U.S. Pat. No. 6,450,419; supporting a bimorph-type transducer on rubber O-rings, e.g. as described in Ross et al U.S. Pat. No. 5,261,601 and Humberstone et al U.S. Pat. No. 5,518,179; and holding the piezoelectric ring in place with a grommet, e.g. as described in Helf et al U.S. Pat. No. 6,293,474 and Tomkins et al U.S. Pat. No. 6,382,522.
The above-described devices translate the radial vibration of a piezoelectric ring to axial vibration of a perforate plate to disperse a liquid as an aerosol. In another type of device, the piezoelectric transducer may be tubular and may expand and contract axially (in the direction of the central axis of the tube) to move a perforate plate. For example, see Newcombe et al U.S. Pat. No. 5,838,350.
Generally, in a piezoelectric transducer that operates in a fluid medium, such as those used in aerosolizers, there is a need to separate the piezoelectric element from the vibratable element so that the vibratable element can be submerged in liquid and the piezoelectric element can be electrically insulated from the liquid. In some cases, such insulation may be provided by encasing the piezoelectric element with elastomer material. Such material, while providing electrical insulation, also has energy-absorbing characteristics that dampen the oscillation amplitude of the piezoelectric transducer and therefore has an adverse effect of the efficiency of the device.
There are currently a wide variety of aerosolizers and nebulizers. Of particular interest are those which vibrate an aperture plate or other element to produce the aerosol. Examples of some of these aerosolizers are described in U.S. Pat. Nos. 5,169,740, 5,938,117, 6,540,154, 5,586,550, 5,750,647, 6,467,476, 6,014,970, 6,755,189, 6,814,071, 6,554,201, 6,732,944, 6,615,824, 6,845,770, and 6,851,626, each of which is incorporated herein by reference in its entirety. One issue with aerosolizers (especially those used for medical applications using highly corrosive liquids) is contamination and corrosion of parts. Certain parts of the aerosolizer that are exposed to liquids may need to be washed or disposed of in order to keep the aerosolizer in good working order. Many of these parts are difficult to clean and, since piezoelectric transducers and their associated electronics can be relatively expensive, making them disposable may not be economically feasible. Therefore, it may be desirable to make certain aerosolizer components removable or replaceable.